17. Rigel (Beta Orionis, Struve 668, double star)
Constellation Orion, also known as the Hunter), magnitude 0.1 / 6.8, separation 9.5”, position angle 202°, RA 05h14m DEC -8°.12’. The primary star, the class B8 supergiant Rigel, is the seventh brightest star in the sky, and it is the brightest star in Orion. In my 8-inch Klevtzov it looks white, but in my 85mm Zeiss reflector, I definitely see a hint of blue. The secondary, using the 8-inch Klevtzov at 166x, also looks bluish-white.

18. Trapezium (Theta Orionis, multiple star)
Constellation Orion (also known as the Hunter), magnitude AB 6.7 / 7.9 and CD 5.1 / 6.7, separation AB 8.8” and CD 13.4”, position angle AB 31° / CD 241°, RA 05h35m DEC -5°23’. This group of blazing young stars, known as the Trapezium, doesn’t need an introduction. The trapezium is a group of four bright white stars at the heart of the Orion Nebula. Even in my 85mm refractor at 30x I can see them as four individual stars, forming a trapezium. The magnitude 5.1 C component stands out from the other three fainter stars in the 85mm reflector. Under a real dark sky, I have seen the E and F component in my 8-inch TAL 200K using medium to high magnifications. This group of stars is just wonderful through almost every telescope.

19. Beta Monocerotis (triple star)
Constellation Monoceros (Unicorn), magnitude 4.7 / 5.2 / 7.1, separation AB 7.3” and BC 2.8”, position angle AB 132° and BC 106°, RA 06h29m DEC -07°02’. Sir William Herschel discovered Beta Monocerotis in 1781, and called it “one of the most beautiful sights in the heavens”, and I can only agree with him. I have been observing this wonderful triple in Monoceros on every possible occasion, just enjoying the view: three almost equally bright stars with the same blue-white color. The A, B and C component form a narrow triangle, and I never found another group of three stars that are so close together, equally bright and of exactly the same color. With my 8-inch telescope I use a magnification of 166x to get a real nice split.

20. Castor (Alpha Geminorum, Struve 1110, triple star)
Constellation Gemini (Twins), magnitude 1.9 / 2.9 / 8.8, separation AB 4.0” and AC 72.5” , position angle AB 68° and AC 164°, RA 07h34m DEC +31°53’. In fact, Castor is a system of six stars. Three of them are visible through amateur telescopes, the A,B and C components. Each of the three visible stars is itself a spectroscopic binary. The faint c-component is in fact a pair of red dwarfs orbiting each other, an eclipsing binary (variable star) designated YY Geminorum. Through my 8-inch telescope at 200x all three components look white.

13. Eta Cassiopeia (S)truve 60, double star)
Constellation Cassiopeia, magnitude 3.4 / 7.5, separation 12.9”, position angle 317°. RA 00h49m DEC +57°49’. This beautiful double was discovered first by William Herschel in 1779. At the moment, both components of Eta Cassiopeiae are separated 12.9”. Calculations based on observations show that the separation varies from 5” (in 1890) to approximately 16” in 2150. The period of the apparent orbit is somewhere between 480 and 520 years. In different observing reports the colors of both components are reported as gold or yellow for the primary and orange or red for the secondary. I only observed it once, under mediocre circumstances, with the 8-inch Klevtzov-Cassegrain. To me they both looked “golden”.

14. Gamma Arietis (Struve 180, Mesarthim, double star)
Constellation Aries (Ram), magnitude 4.8 / 4.7, separation 7.8”, position angle 0°. RA 01h53m DEC +19°18’. Gamma Arietis was probably one of the earliest discovered double stars. Robert Hooke stumbled into it by accident, while following a comet in 1664. Last year, I observed quite a few interesting doubles in Aries myself, but the two white, almost equally bright stars of Gamma Arietis are my favorite. With my 8-inch telescope at 166x both the primary and the secondary look like sparkling white diamonds set against a jet-black sky.

15. Almach (Gamma Andromedae, multiple star)
Constellation Andromeda, magnitude 2.3 / 5.5, separation 9.8”, position angle 63°, RA 02h03m DEC +42°19’. Almach is in fact a multiple star with three components, but the C component can only be detected with larger telescopes. The primary star of Almach is a golden or yellow K2 or K3 type of star, the secondary looks bluish in my 8-inch, but there are many observers that detect a definite green color in the secondary.

16. Iota Cassiopeia (triple star)
Constellation Cassiopeia, magnitude ABC 4.6 / 6.9 / 8.4, separation AB 2.5” / AC 7.2”, position angle AB 230° / AC 114°, RA 02h29m DEC +67°24’. This is one of the finest triple stars that I have observed until now, and it is certainly the most beautiful in the Cassiopeia area. With the 8-inch Tal 200K at 222x I split Iota Cassiopeiae into a bright white primary with a slight hint of yellow, and two white companions showing a hint of blue.

8. Delta 1 and 2 Lyrae (double star)
Constellation Lyra (Lyre), magnitude 5.6 / 4.2, separation 630”, position angle 243°, RA 18h54m DEC +36°55’. Lyra is, like Bootes and Corona Borealis, a treasure trove for observers of double and multiple stars. Delta 1 and 2 Lyrae are a very wide pair of stars that can be observed with handheld binoculars, and in my 15x80 binoculars (mounted on a mirror mount) I can see a bluish-white delta 1 Lyrae and an orange delta 2 Lyrae surrounded by 10 ten fainter stars, forming a star cluster called Stephenson 1. I love to look at this, 16’ wide, open cluster using my 4-inch refractor. At a magnification of 80x to 100x I see about 15 stars. Delta 1 Lyrae and Delta 2 Lyrae are true physical members of this small open cluster.

9. the Double Double (Epsilon 1, and 2 Lyrae, quadruple star)
Constellation Lyra (Lyre), magnitude AB 5.4 / 6.5 and CD 5.1 / 5.3, separation AB 2.6” and CD 2.3”, position angle AB 357° and CD 94°, RA 18h44m DEC +39°40’. The Double Double was the first double/multiple star system I observed with my 8-inch Klevtzov in 2001, and until now the views I got that particular night were the best I ever got from this celestial gem. It was late in august and it had been a very hot and humid day. Around midnight, the outdoor temperature was still above 20 degrees Celsius. There was absolutely no wind and during the daytime, the sky had looked milky-white. During the evening, the air felt heavy and around midnight, the night-sky looked hazy, somehow covered in high cirrus clouds. It seemed useless to get the equipment out for observing, but I just got my new telescope and I couldn’t wait to give it a try. When I pointed the 8-inch TAL at the Double Double, I was stunned by the view. At 166x I saw four bright white stars, of almost equal magnitude, grouped in pairs, two by two. The image looked like the stars where frozen in their position. There was absolutely no movement, no shimmering stars. Both doubles were split perfectly. Later I realized that for observing close double stars, the conditions must have been nearly perfect that night. I observed the Double Double again and again over the last few years, but I never managed to get the same wonderful views I got on that hot night in august 2001.

10. Albireo (Beta Cygni, double star)Constellation Cygnus (Swan), magnitude 3.1 / 5.1, separation 34”, position angle 54°, RA 19h31m DEC 27°58’. In 1978 I followed a course “Astronomy for beginners” at the local astronomy club. The course started in the last week of august and after every lesson, we would go outdoors and look at a few objects through a 4.5-inch reflector. I remember looking at the Andromeda Galaxy, the Double Cluster in Perseus, M13 and ………. Albireo. Until then I had never seen a double star through a telescope, let alone a colored double star! Ever since, I have been looking at Albireo on every possible occasion, with all binoculars and telescopes I ever owned, and I still love to observe this simply beautiful object, even after all these years. Through my 8-inch at 66x the primary, a type-K star, looks golden or yellow. The secondary, a type-B star, looks blue. The contrast, color and brightness of both stars is striking, and this magical double star should be at the top of everyone’s observing list. It is one of the easiest doubles to find and, for me personally, the most beautiful to look at.

11. Omicron 1 and 2 Cygni (31 and 32 Cygni, multiple star for binoculars)
Constellation Cynus (Swan), magnitude 3.9 / 3.9, separation 1°, RA 13h6m DEC +46°44’ (coordinates for Omicron 1). Now this is my favorite multiple star (or group of stars) for binoculars. Through my 15x80, Omicron 1 and 2 Cygni look like two bright orange stars, separated about 1° from each other and of almost equal magnitude. Omicron 1 (31) Cygni is a visual triple itself. About 5’ to 6’ away to the northwest of the orange primary, at a position angle of 323°, I see a bluish (magnitude 4.8) companion and about 100” to the south I see a white (magnitude 6) star at a position angle of 173°. Together, Omicron 1 and 2 Cygni form a wonderful group of four stars to observe with binoculars.

12. 61 Cygni (Struve 2758, double star)
Constellation Cygnus (Swan), magnitude 5.2 / 6.1, separation 30”, position angle 150°, RA 21h07m DEC +38°45’. This is a wide double, which can be separated even in small telescopes and binoculars. Because of their more or less equal brightness, I managed to split 61 Cygni with my 7x50 Bresser mounted on a mirror mount. I never managed to split Albireo in my 7x50, although the angular separation of Albireo is wider (34”), than from 61 Cygni. This is probably caused by the magnitude difference. While Albireo’s components differ about two magnitudes, the brighter A component overpowering the fainter B component, the difference between the 61 Cygni components is only 0.8 magnitude, making it easier to “see” both the primary and secondary as separate stars at low powers. In my 15x80 both the primary and secondary of 61 Cygni look chrome-orange, with a hint of red. Again another celestial gem that shouldn’t be missed!

5. Polaris (Alpha Ursa Minoris, the North Star, the Pole Star, double star)
Constellation Ursa Minor, (Little Bear), magnitude 2.0 / 8.2, separation 18.4”, position angle 218°, RA 02h32m DEC +89°16’. This star is without question one of the best-known stars in the sky, but I wonder how many people know that Polaris is also a very nice double star. Through my 8-inch TAL at 133x, the primary looks yellow and the much fainter secondary looks white. Use medium to high magnification (at least 100X) to split the faint secondary from the bright primary. At low magnifications the secondary is lost in the glare of the primary. If you have an equatorial mount, you might find it difficult to get Polaris into view. You should polar align your mount exactly, or simply turn your polar axis about 90 degrees to the east or west, using your mount more or less as an alt-azimuth mount, and it shouldn’t be too difficult to get Polaris in the centre or the eyepiece. I use the exact polar align method.

6. Epsilon Boötis (Struve 1877, Mirak or Izar, double star)
Constellation Bootes (Herdsman), magnitude 2.9 / 4.9, separation 2.8”, position angle 339°, RA 14h45m DEC +27°04’. In Bootes and the neighboring constellation Corona Borealis I observed quite a few double stars, but Epsilon Boötis, nicknamed Pulcherrima (in Latin: the beautiful) by F. Struve in 1829, is definitely my favorite. Through my 8-inch TAL at 166x this wonderful double has a bright yellow primary and the secondary is white with a slight hint of blue or green. I cannot decide on the color of the secondary. Which color do you see?

7. Ras Algethi (Alpha Herculis, double star)
Constellation Hercules, magnitude 3.5 / 5.4, separation 4.7”, position angle 107°, RA 17h15m DEC +14°23’. This beautiful double in the lower right part of Herculis is again a really good example of the simple beauty of double stars. Through my 8-inch TAL at 133x the primary is orange and the secondary looks white with a hint of green. Now, I know that there are no “green stars”, but it’s just the way the secondary of Alpha Herculis looks to me through the eyepiece. Color perception depends on a lot of different factors, the contrasting colors of stars being one of them. But also the equipment, the local seeing, and last but not least the observer, and the condition he is in, have an influence on color perception. I noticed during star parties and observing sessions with other observers from the local astronomy club, that observing star colors is a very subjective, personal matter. What looks green to one person looks blue to the other. You get the same discussion with yellowish stars. Some see them just as plain white, others as yellow, golden or orange, and some even see them as red.

I can only give you the advice to record the colors what you observed yourself, no matter what others claim to “see” . Write down your own perception in your observing log. Again, seeing colors is a very subjective thing. You best remember your observation, if you write down what you saw, not what others tell you they saw.

During the last few years I “re-discovered” a group of objects that is not as badly affected by light- and air pollution as other deepsky objects: double and multiple stars. Many hundreds if not thousands can be observed from my own suburban backyard, and almost every time I point my telescope on a double or multiple star for the first time, I am in for a big surprise. There are a lot of different factors that can turn a double or multiple star into a true celestial gem. Their components often have beautiful contrasting colors or they show a huge difference in the magnitude. But also a very close couple or group of stars of the same color and/or almost equal magnitude can look simply stunning.

There is no way to catch the telescopic views of double and multiple stars on a photograph, without destroying the aesthetic beauty of these truly sparkling stellar gems. On photographs stars turn into more or less disk-shaped blurry blobs of light. Gone are the sparkling colors, the point-like star-images and the stunning differences in magnitudes. So no matter where you live, whether in the city, somewhere in the suburbs or in a rural area, go out and observe them with your own eyes, using binoculars or a telescope. Only then you will “see” the real beauty that this often neglected group of deepsky objects has to offer.

Anyway, I always have been a visual observer of the deepsky, and I just love these little gems for their aesthetic beauty. So here is my personal top 20 of double and multiple stars (until now), including basic data (constellation, magnitude of all components, separation, position angle, the RA/DEC (right ascension / declination coordinates), some background information, what to expect at the telescope and or binoculars, and of course finder charts for all 20 stars.

I present my 20 favorite double / multiple stars in five consecutive articles, for every time of the year a separate one, starting with early spring constellations and ending with winter constellations. The articles will be published in this blog within the next 6 weeks, starting today. So if you are interested in observing some wonderful double and multiple stars, hop in every now and again to read or print out the series of articles. With this first article, you can start observing double and multiple stars tonight. Clear skies!

My 20 favorite double stars part 1: early spring

1. Iota 1 Cancri (Struve 1268, double star)
Constellation Cancer (Crab), magnitude 4.2 / 6.6, separation 30.5”, position angle 307°, RA 08h54m DEC +28°46’. Cancer is a very faint constellation, but it holds some great open clusters and double stars. Most of you will know M 44, the beehive cluster and M 67, another fine open cluster in Cancer. But at the northern end of the crabs figure you can find iota Cancri, my favorite object in this barely noticeable constellation. Iota Cancri is a magical double, and it could easily be called the “Albireo” of spring. In my 8-inch at 100x it is an striking golden-blue pair of stars. Wonderful! A hidden treasure of the night sky that should be on everyone’s deepsky observing list.

2. Algieba (Gamma Leonis, Struve 1424, double star)
Constellation Leo (Lion), magnitude 2.2 / 3.5, separation 4.4”, position angle 127°, RA 10h20m DEC +19°51’. The name of this star could be from the Arabic “Al Jabha”, the forehead or from the latin word “iuba(e)”, the manes (of the lion). Algieba is the brightest star in the lion’s mane. It consists of a very close pair of stars, but I split the double at 133x with an 8-inch telescope easily. Both the primary and secondary look yellow to me. If you have a small telescope and find it difficult to split this close double, try it in twilight or with moonlight. This often seems to help with splitting bright close pairs, because the glare of the star is reduced. I even read a report from a German observer who got the best results by observing Algieba in a clear blue autumn sky in broad daylight, using a 63mm telescope. To be honest, the only star I ever saw in daylight was the Sun, so maybe I should give it a try.

3. Cor Caroli (Alpha Canum Venaticorum, Struve 1692)
Constellation Canis Venatici (Hunting Dogs) magnitude 2.9 / 5.5, separation 19.4”, position angle 229°, RA 12h56m DEC +38°19’. Cor Caroli, the Heart of Charles, marks the position of one of the two hunting dogs, Chara. Beta Canum Venaticorum marks the other dog, Asterion. Cor Caroli is a fine double and very easy to split in small telescopes. In my 4-inch refractor (TAL) at 83x I definitely see two white stars of unequal brightness. Others report two yellowish stars. Which colors do you see? If you’re not sure, turn the focuser slightly until the stars are out of focus, looking more or less like disks, making color detection easier.

4. Mizar and Alcor (79 Zeta Ursae Majoris and 80 Ursae Majoris, double star)
Constellation Ursa Major (Great Bear) magnitude 2.4 / 4.0, separation 708”, position angle 71°, RA 13h24m DEC +54°56’. Alcor and Mizar both can be seen with the naked eye from my suburban backyard, and it was the first double I pointed my very first telescope (a 4.5 inch reflector) at in 1978. In this small telescope, Alcor and Mizar were both separated widely and placed in the opposite ends of the field of view, and to my surprise Mizar was a double star itself. Mizar’s secondary with a magnitude of 3.9, can be seen at a position angle of 150° and the separation between Mizar A and B is 14.4”. To me, Alcor, Mizar A and B all appear to be white.

Just after dinner we saw a double rainbow right above the street where we live. I rushed outside to find the pot of gold at the end of the rainbow, but once I was outdoors, I decided that the view was too beautiful to be ignored. I quickly grabbed my camera and shot a few images and after that, I simply enjoyed the view. The new telescope will have to wait a littlle longer (sigh).

In the last few weeks I collected some basic lunar data from different online resources and books. I allways find it handy to have this kind of related data grouped together. Click on the image below to enlarge. Of course you are free to download and print the fact sheet. Just click on this link to download the PDF.

I just had my blog updated by Mel from "emtwo webstudios". There were a few minor (security) problems with the blog, and I'm glad that they everything is working fine again. Maybe this is the good time to tell you how to search my blog and how to post comments, because both features have been updated. At the end of the article you will find how to register for my newsletter.

Searching items in Clear Skies On Demand
There are three ways to search certain items in my blog. All three options can be found in the sidebar of the blog: Categories, Archives and Search. I will try to explain the differences between the different search methods.

Categories
You can browse through the categories and subcategories the same way you would browse through a directory structure on a hard drive. For instance, if you want to read about my solar observing sessions, just click on the subcategory “Solar log" in the category “Sun". All articles with solar observing reports will appear in the main window on the right. They will appear sorted by date. The newest entry is always at the top, the oldest at the bottom of the last page.

Archives
You can browse all entries that are in the blog, by browsing through the archives. All entries are in a SQL database, and you can browse through them by date or by category. Just click on “Monthly Archive Listing" or “Category Archive Listing" and a list will appear, with all article titles sorted by date, or by category. I personally use the Category Archive Listing a lot. It shows all the entries per Category, listed alphabetically.

Search
This is the most powerful option to find a certain item you are looking for. Simply type in the text, for instance Copernicus or Herschel, and all entries in which this word is used will appear in a list with the title, the first lines of text of the entry and the author and date. You can go the article you want to read by clicking on the title. The search option really searches the complete database, and if a word is used somewhere in this blog, the entry will appear in the listing. If you get too much search results, narrow down your search by clicking on “Advanced Search" beneath the search window.

Posting comments
This option has been corrupted (some security issue) during the last few months, but thanks to Mel it works just fine again. How can you post a comment?

You first have to be registered as a member of my blog. You can register by clicking on “Register" in the menu at the top right of the header. Once you are registered you receive an e-mail to activate your registration. When your membership is activated you can login by clicking on “Login" in the menu at the top right of the header. When you are logged in you can post comments, and to be honest, comments are highly appreciated! Maybe I can use them to help me making the content better and more interesting for you, so feel free to log in and let me hear what you think!

Newsletter
A lot of people asked me "am I not registered, I subscribed to your newsletter". This is something completely different. Subscribers to my newsletter get an e-mail on a regular basis, with the most recent updates from my blog. People who become registered members can post comments. So if you also want to subscribe to my newsletter, you can do this by clicking on "subscribe here" under "About" at the top of the sidebar.